Creating a character for your novel or short story is more than just writing out a description of the character. It's more like meeting a new person or finding a part of your own personality that you had zero knowledge of. Fragments of their personality won't come to you all at once. They'll seep through the empty cracks and begin to form together. Good characters will literally construct themselves.

When you first 'meet' your character, interview him/her with questions. What is your hair color? What color eyes do you have? How tall are you? Along those lines. Get to know them, put them through different scenarios and see how it plays out. Don't give them a set personality or a base of guidelines because they won't follow them. Learn everything you can about them even if you don't use every physical description in your writing. And eventually they'll become so vivid in your mind that you'll start hearing their voice.

On the other hand sometimes a character comes to you and introduces themselves to you. I recently had a personality come to me while meditating on my work as I do every day. He told me his name and was very defined in the way he talked. Sometimes you think you're going crazy but in the end it'll all work out for the best. Don't be afraid to let a personality come to you, it may be the greatest one yet!